Printing apparatuses are known, of the laser or inkjet type for example, for printing on substrates such as paper, cardboard, polymer sheets or panels, tiles, posters or suchlike, substrates used in the most various fields, for example also medical, and on different types of materials of the substrate, generally comprising one or more printing units installed above a slider and a support plane, for example a belt, a plane or a mat, in which the article to be printed is positioned and possible made to advance, in cooperation with the printing unit.
A plurality of printing heads are installed on the printing units, each of which is provided with delivery nozzles disposed reciprocally in a coordinated manner, in order to carry out the correct printing sequence with the pre-set materials and colors.
The printing head can also be provided, or cooperate, with a drying device, normally a UV lamp or other similar or comparable device (NIR lamp, IR lamp, UV led lamp), to dry the color as print material at the end of the corresponding cycle substantially instantaneously.
Each of the printing heads allows to deliver a color, for example the base colors (cyan, magenta, black and yellow), the additional colors (white), as well as possible specific materials in order to confer, for example, shiny/opaque effects or to deposit additives such as glitter.
In order to perform the printing correctly, a precise and reciprocal positioning of the printing heads is required so that they are correctly aligned with each other, or located parallel with each other, and/or are disposed so that the respective delivery nozzles are located one in continuation of the other, avoiding the presence of zones or lines comprised in the print area of the apparatus, not covered by the ink, or zones where there is an overlapping of deposited print material.
The precision positioning of the printing heads can be obtained mechanically or with electronic adjustment devices.
With regard to mechanical adjustment, an extremely precise working of the support plate is required, with accurate working tolerances, to define reference or abutment planes for the precise positioning of the individual printing heads. The reference or abutment planes are made in coordinated manner on the printing heads too. This solution, however, is extremely expensive and is not usually used, because it is not very reliable and has little possibility of achieving high precision.
Electronic adjustment modes do not allow very sophisticated and precise adjustments either, so that they are adopted only in fields where precision is not so important, for example where water ink printers are used, or where printing occurs for example on a substrate like ceramic.
On the contrary, in fields where print precision is fundamentally important, such as for example in UV printing, considerably more precise and accurate adjustment systems must be used.
In addition, electronic adjustment systems of the linear type are known, that is, which allow to perform translations of the printing heads with respect to the support plate, but do not allow for example an angular adjustment.
It is also known that in the state of the art there are a posteriori adjustment modes, that is, where the printing heads adapt to the position during their use, but a priori adjustment systems do not exist, that is, where the position of the printing heads is imparted before the printing operations.
It is also known that the printing unit can be moved vertically toward/away from the belt or mat to position the printing heads at the correct distance from the support or from the article to perform the printing.
Each printing unit can perform one, two or more successive printing cycles. As the printing cycles increase, so does the definition of the printed image.
A typical disadvantage of known solutions is due to the fact that if there is a need to perform maintenance and/or replacement of a printing module, the whole series of printing units must be replaced. This disadvantage is at least partly due to the fact that it is impossible to adjust the printing heads effectively, precisely and mechanically.
Another disadvantage found in known printing apparatuses is that, to perform even minor operations, such as adjustment of the printing heads or removing a printing module for replacement, it is necessary to use a qualified technician or person of skill in the art, for example the technical assistant of the printing apparatus, making these operations expensive and causing long machine downtimes.
Another disadvantage is that, since the adjustment that can be made on the printing heads once the printing apparatuses have been assembled is minimal, the operations to produce and obtain their constituent parts must be very accurate and with minimum tolerances, thus making the mechanical workings very difficult, long and excessively expensive.
Another disadvantage is that in the state of the art printing apparatuses are made which are bulky in size and of considerable weight.
Another disadvantage of known printing apparatuses, if they consist of several printing units, is the objective impossibility of aligning the printing units, for example in a direction transverse to the printing direction, so as to have a suitable continuity and absence of interruptions or hindrances.
Due to the difficulty of adjusting the printing heads, known printing apparatuses have substantially monolithic structures, in which it is difficult to intervene on a single printing unit or a single printing head.
There is therefore a need to perfect a printing apparatus that can overcome at least one of the disadvantages of the state of the art.
In particular, one purpose of the present invention is to supply a printing unit of the modular type, comprising a plurality of printing units, in which each printing unit can be replaced individually while still guaranteeing precision and reliability in printing, making the apparatus extremely versatile, flexible and compact.
Another purpose of the present invention is to supply a printing apparatus, of the laser or inkjet type for example, for printing on substrates, which allows to adjust, precisely and reliably, the position of the printing head or heads with which each printing unit is provided. Another purpose of the present invention is to obtain a printing apparatus in which the position of each printing head of each printing unit can be adjusted quickly and easily by the operators, for example limiting or preventing the removal of components of the printing apparatus.
Another purpose of the present invention is to obtain a printing apparatus in which the printing head can be adjusted by non-specialized personnel.
Another purpose is to obtain a printing apparatus that allows to make precise, defined, well performed and quick prints.
Another purpose of the present invention is to obtain a printing apparatus comprising a plurality of printing units which can be aligned without interruptions or hindrances in any direction, even a direction substantially orthogonal to the direction in which the support to be printed moves.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.